Heating system for cellulose digestion plants



1959 c. F. ROSENBLAD 2,886,483-

HEATING SYSTEM FOR CELLULOSE DIGESTION PLANTS Filed May 25, 1954INVENTOR. e 7' F 055N494 A 0 United e$tates Patent HEATING SYSTEM FORCELLULOSE DIGESTION PLANTS 'Curt Fredrik Rosenblad, Princeton. N.J.,assignor to, Aktlebolaget Rosenblads Patenter, Stockholm, SwedenApplication May 25, 1954, Serial No. 432,243 Claims priority,application Sweden May 27, 1953 2 Claims. (Cl. 162-42) This inventionrelates to systems for indirect heating of the digestion or boilingliquid in the production of cellulose pulp.

In a system comprising two separate digesters each of which is heatedduring other periods of time than the other digester, it is an object ofthe invention to provide an arrangement enabling both digesters to beheated from a single heater to the effect that the heating surface ofsaid heater which during heating of one of the digesters has been incontact with and subjected to scale formation from the digestion liquidwill be subjected to cleaning action during the heating of the otherdigester and vice versa.

One embodiment of the invention is shown diagrammatically and by way ofan example on the accompanying drawing.

In the drawing A and B indicate two digesters which are heated from acommon heater 1. This heater is provided with two passage systems 2a and2b respectively separated by means of a heat transferring wall 3. Thedigester A is provided with a circulation system for digestion orboiling liquid comprising pipes 4a and 5a. a pump 6a and a valve 701.The digester B is connected to a similar circulation system, comprisingpipes 412 and 5b, a pump 6!) and a valve 7b. The passage system 211 maybe put in communication with the pipe 5a on both sides of the valve 7aby means of conduits includin valves 8a, 9a, respectively, and thepassage system 21; may be put in communication with the pipe 5b on bothsides of the valve 7b by means of conduits including valves 8b, 9b.respectively. A pipe 10 for heating steam may be put in communicationwith the top part of the passage system 2a or of the passage system 2bthrough a valve 11a or a valve 11b respectively and the bottom parts ofsaid passage systems may be put in communication with a steam trap 13through a valve 12a and a valve 12b respectively. A discharge outletfrom the steam trap 13 is provided with a pump 14 and a discharge valve16 adapted to be operated by a float 17 in the steam trap 13 so as toopen when the condensate level in the steam trap rises and to close onsinking condensate level. Through a pipe line 18 and valves 19a, 19b thedischarge outlet 15 may be put in communication with the top part of thepassage system 2a or the passage system 2b.

The system is operated in the following way. When it is desired to heatthe digester A, valve 7a is shut and the digestion or boiling liquid iscirculated from said digester through pipe 4a, pump 6a, valve 80,passage system 2a, valve 911 and pipe 5a back to the digester. With thevalves 7b, 9b, 11a, 12a and 19a closed, heating steam is supplied to thepassage system 2b through pipe 10 and valve 11b and heating steamcondensate is withdrawing from said passage system 2b through valve 12bto steam trap 13 and pump 14. A quantity of said condensatecorresponding to the quantity of newly formed condensate is thuswithdrawn automatically from the system through valve 1.6 operated bythe float 17. The pump 14 is, however, dimensioned as to be capable ofICC delivering considerably more condensate and the surplus quantity ispassed in recirculation through pipe 18 and valve 19b back to the toppart of the passage system 211.

At the end of the heating period of digester A and when thecorresponding heating period for digester B is to start, the valves nowdescribed are reset so that the valves hitherto open are closed and viceversa. The heat exchanging media will now change passageways with eachother so that the digestion liquid will pass through the elementspreviously passed by the heating medium in the same numerical order, andvice versa. As a result, the digestion liquid in the digester A willcontinue to circulate but is passed through the heater via valve whilethe digestion liquid in digester B will be circulated through passagesystem 2b, at the same time heated from the heating steam which issupplied to passage system 2a to which also the surplus condensate frompump 14 is passed. When the heating period for digester B ends. thevalves are reset anew in the way described. Thus, both passage systemswill convey digestion liquid or heating seam alternatively and, duringeach heating period, the heating surfaces of the heater, which duringthe preceding period were in contact with digestion liquid will beflooded with condensate so as to be cleaned from scale, possibly formedduring the preceding period.

It is of course possible for a person skilled in the art by aid of theinformation now given, to make further modifications within the scope ofthe invention, especially in respect of the pipe and valve combinations.Most eflective is a heater with uniform passage systems as suggested inthe drawing. In many cases suificient cleaning effect from the heatingmedium may be obtained without recirculation of the same. A hot liquidcould be used as heating medium instead of steam etc.

What I claim is:

1. The process of operating an indirect heat exchanger having a twopassage system for alternately heating digestion liquor for one of twoseparate digesters in one of said passages and simultaneously cleaningthe other of said passages which comprises, circulating digestion liquorfrom one of said digesters through one of said passages, and passing aheating and cleaning medium through the other of said passages and thenreversing the process by cutting off the flow of digestion liquorthrough said one of said passages, passing heating and cleaning mediumthrough said one of said passages to provide heat for the other of saidpassages while simultaneously cleaning said one passage, circulatingdigestion liquor from the other of said digesters through said other ofsaid passages to heat said liquor and reversing the process back andforth so that said passages are alternately cleaned and used for thepassage of liquor to be heated so that the build up of scale from saidliquor is prevented.

2. The process as in claim 1 wherein said heating medium is steam andincluding withdrawing and condensing steam from said passages andreintroducing said condensate with fresh steam at the entrance end ofthe passage being used for heating to flood the same with condensateduring the heating to enhance the cleaning of the passage.

References Cited in the file of this patent UNITED STATES PATENTS1,228,950 Morterud June 5, 1917 1,882,391 Morterud Oct. 11, 19322,508,119 Lockman May 16, 1950 2,576,843 Lockman Nov. 27, 1951 2,647,570Lockman Aug. 4, 1953 FOREIGN PATENTS 173,132 ,Canada of 1917

1. THE PROCESS OF OPERATING AN INDIRECT HEAT EXCHANGER HAVING A TWOPASSAGE SYSTEM FOR ALTERNATELY HEATING DIGESTION LIQUOR FOR ONE OF TWOSEPARATE DIGESTERS IN ONE OF SAID PASSAGES AND SIMULTANEOUSLY CLEANINGTHE OTHER OF SAID PASSAGES WHICH COMPRISES, CIRCULATING DIGESTION LIQUORFROM ONE OF SAID DIGESTERS THROUGH ONE OF SAID PASSAGES, AND PASSING AHEATING AND CLEANING MEDIUM THROUGH THE OTHER OF SAID PASSAGES AND THENREVERSING THE PROCESS BY CUTTING OFF THE FLOW OF DIGESTION LIQUORTHROUGH SAID ONE OF SAID PASSAGES, PASSING HATING AND CLEANING MEDIUMTHROUGH SAID ONE OF SAID PASSAGES TO PROVIDE HEAT FOR THE OTHER OF SAIDPASSAGES WHILE SIMULTANEOUSLY CLEANING SAID ONE PASSAGE, CIRCULATINGDIGESTION LIQUOR FROM THE OTHER